The Resting (Polarized) Membrane

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The Resting (Polarized) Membrane

• Potassium Pumps pull K ions into the cell
• Sodium Pumps push Na ions out of the cell
• Potassium diffuses out through potassium
  channels
• more rapidly than
• Sodium diffuses in through sodium channels
• i.e. membrane is more permeable to K than to
  Na
• More positive ions outside the cell than inside
  means
• outside is positive relative to inside
• this results in a
• Resting potential of -70 mV (milliVolts)

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Depolarization
Sodium (Na) channels open while Potassium (K)
channels close Membrane becomes more permeable to
Na than to K
Sodium ions enter the neuron by diffusion and
charge attraction
Charge reversal occurs inside of cell is now
positive relative to outside Charge is now 40 mV
(milliVolts)
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Repolarization
Sodium (Na) channels close while Potassium (K)
channels open Membrane is once again more
permeable to K than to Na
Potassium again diffuses out through potassium
channels more rapidly than Sodium diffuses in
through sodium channels Potassium Pumps pull K
ions into the cell Sodium Pumps push Na ions
out of the cell Membrane potential returns to
resting level of -70 mV
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Nerve Conduction

• Stimulus happens at dendrites and starts action
  potential process
• Axons that transport the electrical signals can
  be very long or very small
• Many, many of these going on at once, happens to
  the same neuron very quickly after refractory
  period

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Nerve Conduction - Intensity

• Considering all or none response, how do we
  perceive intensity???
• 1) Frequency of nerve impulse
• Higher frequency brain interprets as a more
  intense stimulus
• 2) Summation
• Intense stimulus from our receptors can cause
  more than one neuron to reach threshold level and
  create action potential

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Synapse - Basics

• A Synapse is the region between neurons (synaptic
  cleft)
• Very small space but is still there

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Synapse - Basics

• Not for all neurons, some are connected
• Single neuron may branch many times
• Neuron ---------
• May be a synapse between many neurons at the end
  of one (rarely only between 2 neurons)

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Synapse - Process

• Small vesicles containing transmitter chemicals
  are in endplates of axons
• Impulse moves along the axon and chemicals are
  released by the endplates
• Chemicals diffuse across the synapse and starts
  depolarization on that neuron and continues
  (post-synaptic neuron)

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Synapse - Process

• When there is a synapse, the electrical
  transmission of energy is slowed
• The greater the number of synapse between the
  stimulus and the brain, the longer it takes to
  get there
• Reflexs have very few synapses

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Transmitter Chemicals

• Acetylcholine
• typical transmitter chemical found in end plates
• makes the postsynaptic membranes more permeable
  to Na
• Cholinesterase
• enzyme released from end plate of neurons shortly
  after acetylcholine
• breaks down acetylcholine, neuron can recover

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Transmitter Chemicals

• Acetylcholine can be an excitatory or a
  inhibitory transmitter chemical
• Excitatory ones allow impulse to travel
• Inhibitory ones prevent post-synaptic neurons
  from becoming active (important process)

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Transmitter Chemicals

• The interaction of excitatory and inhibitory
  chemicals is what allows you to throw a ball
• Triceps receives excitatory and contracts
• Biceps receives inhibitory and relaxes

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Transmitter Chemicals Disorders

• Inhibitory impulses in your CNS (brain)
• Sensory concentrated on teacher
• Not temperature or clothes, etc.
• Disorders related to transmitter chemicals
• Parkinsons disease
• Involuntary muscle contraction
• Alzheimers disease
• Deterioration of memory and processing
• Decreased production of acetylcholine

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